Refrigeration control system



April A. B. NEWTON REFRIGERATION CONTROL SYSTEM Filed NOV. 28, 1938 131mm for Alwin B.Newi:o:n 3y. I

Uflorngg Patented Apr. 23, 1940 UNITED STATES PATENT OFFICE 2,198,174 REFRIGERATION CONTROL SYSTEM Delaware Application November 28, 1938, Serial No. 242,723

15 Claims.

This invention relates to a multiple fixture mechanical refrigeration system andmore particularly to a system wherein frequent defrosting of the evaporators in the various fixtures is assured.

Many methods have been proposed to control a system of this type, one of these being shown in the application of William L. McGrath, Serial No. 196,446, filed March 17, 1938. In one form of the invention illustrated in this application, a solenoid valve controls the fiow of refrigerant to each evaporator, and a thermostat is located in each fixture to control the associated solenoid valve in accordance with the temperature in the fixture. The thermostats are connected in parallel to the compressor starting circuit and the compressor is maintained in operation as long as any of the thermostats are calling for cooling.

As soon as all the thermostats become satisfied,

the compressor shuts down and cannot become restarted until the suction pressure rises to a predetermined value, which value will not be attained until all of the evaporators have become defrosted. Accordingly, once the compressor has tors become defrosted, but in view of the fact that all of the fixture thermostats must be simultaneously satisfied in order to shut down the compressor, there is no assurance that frequent defrosting of the evaporators will occur. The reason for this is that due to varying load conditions in the various fixtures, a long time may elapse before each of the thermostats is satisfied at the same time since the thermostats will not necessarily cycle together. Accordingly, with this type of system, there is no definite assurance that frequent defrosting of the evaporators will take place.

, The system illustrated in the second form of 40 the invention of the McGrath application is designed to overcome this disadvantage of the above described system. In this arrangement, the thermostats in the various fixtures are arranged as described above, and' a timer is provided to interrupt operation of the compressor at predetermined intervals. Whenever the compressor is shut down by the timer, it cannot be restarted until the suction pressure has risen above the defrosting value, but whenever the compressor is shut down by reason of all the thermostats being simultaneously satisfied, it can be restarted as soon as one of the thermostats again calls for cooling, regardless of the value of the suction pressure, unless the timer has operated in the meantime. Thus, this sysstopped, it cannot be restarted until all evapora-- tem requires the provision of a timer mechanism, and in addition thereto, it has the disadvantage that a defrosting cycle will not commence if all the thermostats should be simultaneously satisfied, unless an operation of the timer mechanism takes place during this time.

In my copending application Serial No. 196,450, filed March 17, 1938, a system is illustrated which is designed to reduce the likelihood of the thermostats in the fixtures cycling in such a manner that they will not all be satisfied simultaneously in a system of the type shown in the first form of the invention of the McGarth application described above. In this application, heating elements are located in heating relationship with the thermostats, these heating elements being imbedded in heat absorbing masses which support the thermostats. During a defrosting period, when all of the thermostats have become satisfied, the heating elements are energized which causes the temperature of all of the thermostats to rise to a value in which they are all calling for cooling. Accordingly, when the suction pressure rises to the desired value at which all the evaporators are defrosted, all of the thermostats will be calling for cooling and the tendency will be for the thermostats to cycle together, and the chance of one or another thermostat always calling for cooling will be greatly reduced. This type of system is not entirely satisfactory however, since in certain cases, the thermostats may still so get out of step thata long time may elapse before a defrosting period starts, so that while this system reduces the danger of infrequent defrosting periods of the first system of the McGrath application, it does not entirely eliminate this danger.

In the application of George H. Fisher, Serial No. 232,606, filed September 30, 1938, a system somewhat similar to that shown in the McGrath application Serial No. 196,446 is illustrated for causing frequent defrosting of a multiple fixture refrigeration system. In this system, a defrosting period will take place whenever the thermostats in all of the fixtures become satisfied at the same time min Figure 1 of the McGrath application, and in addition thereto, a timer is provided to shut down the compressor at definite intervals, thus insuring a defrosting period at definite intervals even if the various thermostats shouldn't become satisfied at the same time often enough to insure frequent defrosting. Tlie compresscr will also shut down if the suction pressure drops to asufiiciently low value. This system requires the provision of a timing mechanism, and

it may very likely happen that the timing mechanism may initiate a defrosting period soon after one has taken place by reason of all the thermostats becoming simultaneously satisfiied, or by reason of the suction pressure dropping to a low enough value, and it is obviously undesirable that defrosting take place when unnecessary.

In accordance with the teaching of my invention, frequent defrosting of the evaporators is assuredfrega rdless of the relative temperature in the variousjfixtures and without the use of heaters with the thermostats or the'use of a timing means. This is accomplished by having the thermostat in only one of the fixtures in control of the compressor, so that whenever the temperature in that fixture becomes satisfied, or the suction pressure in the system drops low enough, the compressor stops and cannot restart until the suction pressure rises to a high enough value to indicate that the evaporators are all defrosted. The temperatures of the other fixtures may be controlled by controlling the flow of refrigerant through the evaporators therein. This may be accomplished by providing a thermostatic expansion valve having an adjustable superheat setting, and adjusting the setting thereof in accordance with the temperature in the fixture to vary the degree of superheat in the evaporator and consequently the effective cooling area thereof. If it is desired to control the fixture to maintain a desired humidity rather than a desired temperature within the fixture, this may be conveniently done by varying the superheat setting. Another way in which the fixture temperature may be readily controlled is by providing an adjustable valve in the supply line to the expansion valve, and adjusting this valve in accordance with the temperature in the fixture to control the flow of refrigerant to the expansion valve.

It is therefore an object of my invention to provide, in a multiple fixture type mechanical refrigerating system a novel control arrangement whereby the conditions in each of the fixtures may be independently controlled and whereby frequent defrosting of all of the evaporators is assured.

Other objects and advantages'will become apparent upon reference to the specification, claims, and appended drawing wherein is illustrated a preferred form of my invention.

Referring more particularly to the drawing, a refrigeration system is illustrated, this system comprising a compressor M, a condenser receiver l2, and evaporators l3, l4, and I5 which are connected in parallel in the system. The evaporators |3, I4, and I5 are located in fixtures |6, I1, and I8, respectively. Expansion valves I9, 20, and 2| control the flow of refrigerant into the evaporators l3, l4, and |5-, respectively, the valves 9 and 2| being illustrated as any conventional form of thermostat expansion valve and the valve 20 as will be pointed out hereinafter being of a type wherein the superheat setting of the valve may be automatically adjusted in accordance with a condition in the fixture l1. When the compressor I is in operation, refrigerant flows through the pipe 22 into condenser from which it flows into the receiver l2 and through the pipe 25 to the various expansion valves and returns by way of the pipe 25 to the inlet of the compressor ||l,: in a manner well known in the art.

The compressor I0 is driven by a motor 3|! and this motor may be controlled by a control device of the type shown and described in application Serial No. 196,447, filed by Albert L. Judson and Carl G. Kronmiller on March 1'7, 1938. For pur poses of illustration, in this application this control device is generally represented by the reference character 3| and ,is shown to comprise a base 32 upon which is mounted a bellows 35. The bellows 35 is connected by a pipe 36 to the low pressure or suction line 26 of the refrigerating apparatus. The bellows 35 operates a lever 31 pivoted on a fulcrum member 38 against the action of a tension spring 39. One end of the tension spring 39 is connected to the lever 31 and the other end is connected to a nut 40 screwthreadedly mounted on a screw 4|. By rotating the screw 4| the tension in the spring 39 is adjusted to calibrate the pressure setting of the bellows 35. The lever 31 carries an insulating pad 42 upon which is mounted a bridge member 43. The bridge member 43 carries a contact 44 which is adapted to engage a resilient contact member 45 carried by a terminal 46. The bridge member 43 also carries a contact 41 adapted to engage a resilient contact member 48 carried by a terminal 49. The contact members 45 and 48 are adjustably positioned by means of concentricall located and independently rotated cams and 5|. By rotating the cam 59 the position of the contact member 45 with respect to the contact member 44 may be varied and likewise by rotating the cam 5| the position of the contact member 43 may be varied with respect to the contact 41. For purposes of illustration it is assumed that the cams 50 and 5| are so positioned that upon an increase in suction pressure the contact 44 engages the contact member 45 at substantially 20 pounds and that the contact 41 engages the contact member 48 at substantially 35 pounds. Upon a decrease in pressure the contact 41 disengages the contact member 48 at 35 pounds and then the ,contact 44 disengages the contact member 45 at 20 pounds. It is assumed that when the pressure in the low pressure or suction line 26 rises to some value, say 32 pounds, that defrosting of the evaporators l3, l4 and I5 has occurred. Accordingly, the contact 41 is not moved into engagement with the contact member 48 until defrosting of all of the evaporators has occurred; Since the low pressure or suction pressure is a direct indication of evaporator temperature, then it may be said that the contacts 44 and 41 are operated in accordance with changes in evaporator temperature. If desired, the bellows 35 could be connected by a capillary tube to a bulb located adjacent one of the evaporators, the bulb contain ing a volatile fluid so that the bellows 35 would be operated in direct accordance with evaporator temperature, or could be connected to a plurality of bulbs, there being a bulb located adjacent eachof the evaporators.

The unitary control arrangement 3| also includes a bellows 53 connected by a pipe 54 to 'the high pressure line 22 of the refrigerating apparatus. The bellows 53 operates a lever 55 fulcrumed on a. fulcrum member 56 against the action of a tension spring 51. One end of the tension spring is connected to the lever 55 and the other end is connected to a nut 58 screw-threadedly mounted on a screw 59., By rotating the screw 59 the tension in the spring 51 may be adjusted to adjust the pressure setting of the bellows 53. The lever 55 carries an adjustable abutment member 59 having abutments 6| and 62. The abutment 5| is adapted to engage a resilient contact member 53 carried by a terminal 64.

Contact member 63 engages a contact 65. The abutment 62 is adapted to engage a resilient contact member 66 carried by the terminal 49. The contact member 66 engages a contact 61. For purposes of illustration, it is assumed that upon an increase in pressure the abutment 62 first engages the contact member 66 to move the contact member 66 out of engagement with the contact 61 when the high pressure rises to 135 pounds and the abutment 6| engages the contact member 63 to move the contact member 63 out of engagement with the contact 65 when the high pressure rises to 185 pounds. Upon a decrease in pressure contact member 63 engages contact 65 at 185 pounds and the contact member 66 engages the contact 61 at 135 pounds.

The unitary control arrangement 3| also includes a relay or starter generally designated at 68. This relay or starter comprises an operating coil 69 for operating a bridge member 18 with respect to maintaining contacts 1| and 12 and a bridge member 13 with respect to load contacts 14 and 15. When the operating coil 69 is energized the bridge member 18 is moved into engagement with the contacts 1| and 12 and the bridge member 13 is moved into engagement with the contacts 14 and 15. ,When the operating coil 69 is deenergized the bridge members 18 and 13 are moved out of engagement with their respective contacts by means of springs, gravity, or other means, not shown.

The unitary control arrangement 3| may also include an overload cut-out generally designated at 11. This overload cut-out may include a heater element 18 connected between a terminal 18 and the load contact 14 for heating a thermostatic element which trips open contacts 88 and 8| upon the occurrence of an overload condition. The contacts 88 and 8| may be manually reclosed by means of a reset arm 82.

Power is supplied to the unitary control arrangement 3| by means of line wires 88 and 89 leading from some source of power (not shown).

.The line wire 88 is connected to the contact 65 and the line wire 89 is connected to the power terminal 86. The compressor motor 38 is connected by wires 98 and 9| across the relay load contact 15 and the power terminal 86. Terminal 46 is connected by means of a wire I88 to an electrode I8I in a mercury switch I82 which is located in the fixture I6. This switch I82 is carried by an arm I83 pivoted at I84 and biased by means of a spring I85 into engagement with the upper portionjof a bellows I86 provided with a suitable volatile fill whereupon this bellows expands or contracts in accordance with variations in temperature in the fixture I6. The other terminal I81 of the switch I82 is connected by means of a wire I88 to the terminal 64. The contact 61 is connected by means of a conductor 8 to the relay maintaining contact 12 which in turn is connected by means of a conductor III to the contact 88 of the overload cut-out 11. The contact 8| is connected by a conductor 2 to the operating coil 69 which is in turn connected by a conductor 3 to the power terminal 86. The bridge member 43 is connected by a conductor I I5 to the relay contact 1|. The contact 65 is connected by a conductor 6 to the terminal 19 of the overload cut-out 11.

Assuming the parts in the position shown, the high pressure is less than 135 pounds, the low pressure is less than pounds, and the temperature of the fixture I6 is less than 48, hence the relay or starter 68 is dropped out and the compressor is not operating. Assume now that the low pressure rises to 35 pounds by reason of the defrosting of all of the evaporators and that the temperature within the fixture I6 rises to 48. When this occurs, a starting circuit is completed from the line wire 88 through contact 65, contact member 63, terminal 64, wire I88, electrodes I81 and MI of the switch I82, wire I88, terminal 46, contact member 45, contact 44, bridge member 43, contact 41, contact member 46, contact 61, conductor 8, contact 12, conductor ||I, contacts 88 and 8| of the overload cut-out 11, conductor 2, operating coil 69, conductor H37 and power terminal 86 back to the other line wire 89. Completion of this starting circuit energizes the operating coil 69 to move the bridge member 18 into engagement with the maintaining contacts 1| and 12 and to move the bridge member 13 into engagement with the load contacts 14 and 15.

Movement of the bridge member 13 into engagement with the load contacts 14 and 15 completes a load circuit for the compressor motor 38 which may be traced as follows: from the line wire 88 through contact 65, conductor 6, terminal 19, heater 18, contact 14, bridge member 13, contact 15, wire 98, compressor motor 38, wire 9| and power terminal 86 back to the other line wire 89. Completion of this load circuit causes operation of the refrigerating apparatus.

Movement of the bridge member 18 into engagement with the maintaining contacts 1| and 12 completes a maintaining circuit for the operating coil 69 which is independent of the contact members 48 and 66 and this maintaining circuit may be traced from the line wire 88 to contact 65, contact member 63, terminal 64, wire I88, electrodes I81 and IN, wire I88, terminal 46, contact member 45, contact 44, bridge member 43, conductor II5, contact II, bridge member 18, contact 12, conductor III, contacts 88 and BI, conductor II2, operating coil 69, conductor 3 and power terminal 86 back to the line wire 89. Completion of this maintaining circuit for the relay or starter 69 maintains the refrigerating apparatus in operation until either the temperature of the fixture I6 decreases to'38, for example, the low pressure decreases to 20 pounds, or the high pressure increases to 185 pounds. After the compressor has been shut down upon the occurrence of any of these contingencies, it cannot be again restarted until the high pressure decreases to 135 pounds, the low pressure increases to 35 pounds, and'the temperature of the fixture I6 increases to By reason of this control arrangement the temperature of the fixture I6 is normally maintained within the desired limits of 38 to 40 and the defrosting occurs each time that the operation of the refrigerating apparatus is stopped, this defrosting taking place in all of the evaporatorssince the bellows 35 responds to the suction pressure in the Whole system and this suction pressure will not rise to 35 pounds until all of the evaporators have defrosted.

Located within the fixture I1 is a humidity responsive device I25, this device comprising a humidity responsive element I26 of any conventional construction being suitably secured to a support atitslower end and having its upper end secured to one end of a lever I21, this lever being biased in a direction which maintains the humidity responsive element elongated by means of a spring I28. Carried by the lever I21 is an arm I29 which is arranged to sweep over a potentiometer resistance I38. Upon an increase in humidity within the fixture II, the element I26 will expand and permit movement of the arm I29 to the right under the influence of the spring I 28 and upon a decrease in humidity in the space the arm I29 will move to the left by reason of the contraction of the element I26. The potentiometer I39 is arranged to control a motor I3I which may be a proportioning motor of the type illustrated in Patent No. 2,928,110 issued to D.-G. Taylor on January 14, 1936. The outer terminals of this motor are connected by means of conductors I32 and I33 to the extremities of the re sistance I39 and the center terminal of the motor is connected by the conductor I34 to the slider arm I29. Conductors I35 and I39 are provided for supplying power to the motor I3I. Operated by the motor is a pinion I39 carried by the shaft I39 of the motor and upon reference to the Taylor patent, it will be apparent that movement of the arm I29 with respect to the resistance I39 will cause rotation of the pinion I39 by an amount which is proportional to the movement of the arm I29. This motor I3I is provided for varying the superheat setting of the expansion valve 29 in accordance with variations in humidity in the fixture II as will now be described.

The expansion valve 29 may be any one of the types shown in my copending application Serial No. 192,818, filed February 26, 1938. This valve has provisions whereby the superheat setting thereof may be readily varied, there being an adjustable yoke I49 biaseddownwardly by means of a spring I4I, the upper portion of the spring hearing against an adjusting nut I45 movable with the valve, and the lower portion of the spring bearing against the lower portion of the yoke ,(not shown) and biasing the yoke downwardly, the yoke terminating in a rack I42 which meshes with the gear I38. The expansion valve is moved in accordance with variations in superheat at the outlet of the evaporator, the operating parts of the valve responding to the pressure of the refrigerant leaving the evaporator and also responding to the pressure corresponding to the temperature of the refrigerant leaving the evaporator. For this purpose a connection I43 is provided between the valve and the evaporator outlet by which variations in pressure are communicated to the operating portions of the valve. Within this connection may be provided a capillary tube terminating in a bulb having a volatile fill which may be located within the outlet pipe of the evaporator I I in order to communicate the eifects of temperature variations in the evaporator outlet as .shown in my bopending application referred to above. As the rack I42 is moved upwardly against the force of the spring I4I, it causes an increase in the superheat setting of the valve which means that the valve will maintain a higher superheat at the outlet of the evaporator and a smaller portion of the evaporator will be filled with liquid refrigerant but this liquid refrigerant will be at a lower pressure so'th'at while the temperature of the evaporator is reduced by moving the rack I 42 downwardly the effective cooling area thereof is at the same time decreased. By causing a reduction in the pressure of the refrigerant, the temperature of the other evaporator will also be reduced to increase the cooling effect thereof, and cause the system to operate at maximum efliciency.

As the humidity in the fixture I'I rises and the arm I29 moves to the right, it will cause operation of the motor in amanner tocause upward movement of the rack I42 by an amount which is proportional to the rise in humidity which'willraise the superheat setting of the expansion valve 29 causing the evaporator I4 to operate at a higher superheat but at a lower coil temperature thus increasing the dehumidifying effect of the evaporator I4. While I have shown the control of the expansion valve 29 in the fixture IT by a humidity responsive device to maintain a predetermined humidity within the fixture, it will, of course, be obvious that this humidity responsive element might be replaced by a temperature responsive device if it were desired to maintain the temperature in the fixture at a predetermined value, in which case upon a rise in temperature in the space the rack I42 would be moved downwardly thus decreasing the superheat setting of the expansion valve whereupon the evaporator I4 would be operated at a lower superheat and a larger portion of the evaporator would be effective for sensible cooling. It will be understood that the limit of the superheat maintained by any evaporator will be determined solely by the setting of the expansion valve for that evaporator.

Another way in which the control of the fixture temperature may be readily effected is illustrated in the fixture I8. The flow of refrigerant to the evaporator I5 in this fixture is shown as being controlled by the expansion valve 2| which may be any conventional type of thermostatic expansion valve whereupon the evaporator will be operated at a substantially constant degree of superheat. A second valve I59 controls the flow of refrigerant to the expansion valve 2I, the position of this valve I59 being controlled by an operating diaphragm I5I. The pressure exerted on the diaphragm I5I is varied in accordance with the temperature in the fixture and fixture I8 and in turn will cause movement of the diaphragm I5I and the valve I59. Upon an increase in temperature in the fixture I8, the' pressure exerted by the volatile fill will de ease and the valve I49 will move to a position wherein a greater fiow of refrigerant to the expansion valve 2I is permitted to increase the cooling effect of the evaporator I5. Thus the cooling effect of the evaporator I5 and the temperature of the fixture I8 may be readily controlled by operation of the valve I49 in the line leading to the expansion valve 2I.

The operation of this system will now be readily apparent. The fixture I6 may be the one having the greatest load requirements and may be a large fixture such as a walk-in box and for this reason the temperature controller I95 is located therein. The other fixtures I1 and I8 may be for any suitable purpose such as display cases, water coolers, and the like, and having a lesser load requirement on the refrigeration system. As soon as the temperature within the fixture I8 rises sufficiently high and the suction pressure in the system rises sufiiciently high, say to pounds, at which pressure all the evaporators are defrosted, the compressor will be placed in operation and refrigerant will be supplied to all of the evaporators. The temperature of the fixture I8 is controlled by controlling the valve I59 which controls the amount of refrigerant supplied to the expansion valve 2| and the humidity or, if desired, the temperature of the fixture II is controlled by controlling the degree of superheat in the evaporator M by adiusting the superheat setting of the expansion valve 20. As long as the temperature within the evaporator I6 is above the desired value, the compressor will continue operating unless the suction pressure in the system should fall below 20 pounds or the head pressure should rise above 185 pounds. It is advisable to maintain the compressor in operation until the temperature in the fixture l6 drops to the desired value since this is the fixture that will normally require the greatest amount of cooling and it is therefore not desirable to commence a defrosting cycle until the temperature of this fixture had dropped to the desired value. As soon as the thermostat in the fixture I6 is satisfied, however, the compressor will shut down and cannot be restarted until the suction pressure throughout the system rises to 40 pounds, at which pressure all of the evaporators will be defrosted so that a defrosting cycle is assured between each operation of the compressor. The expansion valves operate to prevent fiooding of the evaporators during the defrosting cycle since they operate to control the superheat at the outlets thereof.

It will be obvious that the temperature con troller of the fixture l8 may take any desired form and the valve I40 may be controlled by a proportioning motor as shown in the fixture I! or in any other suitable manner. Suitable adjustments may be made so that the temperatures inthe various fixtures or the humidity in the fixture I! may be maintained at any desired value.

It will thus be seen that frequent defrosting oi the system is assured without the use of any timing mechanism and without depending upon a plurality of fixture thermostats cycling together since it is necessary for only the thermostat in the main fixture to become satisfied to initiate a defrosting operation and this is made possible by reason of the fact that the temperatures in the other fixtures are adjusted or controlled by controlling the flow of refrigerant into these other evaporators.

Having described a preferred form of my invention, it will be understood that many modifications may be made therein and I therefore desire to be limited only by the scope of the appended claims.

I claim as my invention:

1. In a multiple fixture mechanical refrigerating apparatus having an evaporator for each fixture, a condenser and a compressor for circulating refrigerant through the evaporators, means responsive to the temperature of one of the fixtures for starting and stopping operation of the compressor to maintain desired temperature con-" ditions within said fixture, means responsive to a condition to be controlled in another fixture for controlling the flow of refrigerant through the evaporator in that fixture to maintain the condition therein at a desired value, and means for always preventing restarting of the compressor until all of the evaporators have been defrosted.

2. In a multiple fixture mechanical refrigerating apparatus having an evaporator for each fixture, a condenser and a compressor for circulating refrigerant through the evaporators, means responsive to the temperature of one of the fixtures for starting and stopping operation of the compressor to maintain desired temperature conditions within said fixture, suction pressure responslve means in control of said compressor for interrupting operation thereof whenever the suction pressure drops to a predetermined value, means responsive to a condition to be controlled in another fixture for controlling the flow of refrigerant through the evaporator in that fixture to maintain the condition therein at a desired value, and means for always preventing restarting of the compressor until all of the evaporators have been defrosted.

3. In a multiple fixture mechanical refrigerating apparatus having an evaporator for each fixture, a condenser and a compressor for circulating refrigerant through the evaporators, means responsive to the temperature of one of the fixtures for starting and stopping operation of the compressor to maintain desired temperature conditions within said fixture, means responsive to the temperature in another fixture for controlling the fiow of refrigerant through the evaporator in that fixture to maintain the temperature therein at a desired value, and means for always preventing restarting of the compressor until all of the evaporators have been defrosted.

4. In a multiple fixture mechanical refrigerating apparatus having an evaporator for each fixture, a condenser and a compressor for circulating refrigerant through the evaporators, means responsive to the temperature of one of the fixtures for starting and stopping operation of the compressor to maintain desired temperature conditions within said fixture, means responsive to the humidity in another fixture for controlling the fiow of refrigerant through the evaporator in thatfixture to maintain the humidity therein at a desired value, and means for always preventing restarting of the compressor until the suction pressure has risen to a predetermined value whereby simultaneous defrosting of the evaporators is effected.

5. In a multiple fixture mechanical refrigerating apparatus having an evaporator for each fixture, a condenser and a compressor for circulating refrigerant through the evaporators, means responsive to the temperature of one of the fixtures for starting and stopping operation of. the compressor to maintain desired temperature conditions within said fixture, suction pressure responsive means in control of said compressor for interrupting operation thereof whenever the suction pressure drops to a predetermined value, means responsive to the temperature in another fixture for controlling the fiow of refrigerant the compressor until the suction pressure has risen to a predetermined value whereby simultaneous defrosting of all the evaporators is effectedf.

6. In a multiple fixture mechanical refrigerating apparatus having an evaporator for each fixture, a condenser and a compressor for circulating refrigerant through the evaporators, means responsive to the temperature of one of the fixtures for starting and stopping operation of the compressor to maintain desired temperature conditions within said fixture, suction pressure responsive meansin control of said compressor for interrupting operation thereof whenever the suction pressure drops to a predetermined value, means responsive to the humidity in another fixture for controlling the fiow of refrigerant through the evaporator in that fixture to maintain the humidity therein at a desired value, and means for always preventing restarting of the compressor until the suction pressure has risen to a predetermined value whereby simultaneous defrosting of all the evaporators is effected.

7. In a multiple fixture mechanical refrigerating apparatus having an evaporator for each fixture, a. condenser and a compressor for circulating refrigerant through the evaporators, means responsive to the temperature of one of the fixtures for starting and stopping operation of the compressor to maintain desired temperature conditions within said fixture, thermostatic expansion valve means controlling the flow of refrigerant through the evaporator in another fixture, means responsive to a condition to be controlled in that fixture for adjusting the superheat setting of said valve means to control the fiow of refrigerant thereto to maintain the condition in that fixture at a desired value, and means for always preventing restarting of the compressor until the suction pressure has risen to a predetermined value whereby simultaneous defrosting of all the evaporators is effected.

8. In a multiple fixture mechanical refrigerating apparatus having an evaporator for each fixture, a condenser and a compressor for circulating refrigerant through the evaporators, meansresponsive to the temperature of one of the fixtures for starting and stopping operation of the compressor to maintain desired temperature conditions within said fixture, thermostatic expansion valve means controlling the flow of refrigerant through the evaporator in another fixture, a second valve means controlling the flow of refrigerant to said expansion valve means, means responsive to a condition to be controlled.- in that fixture for adjusting said second valve means whereby the fiow of refrigerant through the evaporator in that fixture is properly controlled to maintain the condition therein at a desired value, and means for always preventing restarting of the compressor until the suction pressure has risen to a predetermined value whereby simultaneous defrosting of all the evaporators is effected.

9. In a multiple fixture mechanical refrigerating apparatus having an evaporator for each fixture, a condenser and a compressor for circulating refrigerant through the evaporators, means responsive to the temperature of one of the fixtures for starting and stopping operation of the compressor to maintain desired temperature conditions within said fixture, suction pressure responsive means in control of said compressor for interrupting operation thereof whenever the suction pressure drops to a predetermined value, thermostatic expansion valve means controlling the fiow of refrigerant through the evaporator in another fixture, means responsive to a condition to be controlled in that fixture for adjusting the superheat setting of said valve means to control.

the fiow of refrigerant thereto to maintain the condition in that fixture at a desired value, and means for always preventing restarting of the compressor until the suction pressure has risen to a predetermined value whereby simultaneous defrosting of all the evaporators is effected.

10'. In a multiple fixture mechanical refrigerating apparatus having an evaporator for each fixture, a condenser and a compressor for circulating refrigerant through the evaporators, means responsive to the temperature of one of the fixtures for starting and stopping operation of the com pressor to maintain desired temperature conditions within saidfixture, suction pressure responsive means in control of said compressor for interrupting operation thereof whenever the suction pressure drops to a predetermined value, thermostatic expansion valve means controlling the fiow of refrigerant through .the evaporator in another fixture, a second valve means controlling the fiow of refrigerant to said expansion valve means, means responsive to a condition to be controlled in that fixture for adjusting said second valve means whereby the flow of refrigerant through the evaporator in that fixture is properly controlled to maintain the condition therein at a desired value, and means for always preventing restarting of the compressor until the suction pressure has risen to a predetermined value whereby simultaneous defrosting of all the evaporators is efiected.

11. In a multiple fixture refrigerating apparatus having an evaporator for each fixture, a condenser and a compressor for circulating refrigerant through the evaporators, control means for said compressor, said control means including means for starting the compressor whenever the temperature in one of said fixtures rises above a predetermined value, the suction pressure rises above a value indicating that all of the evaporators are defrosted, and the head'pressure on the compressor drops below a predetermined value, means for interrupting operation of the compressor whenever the temperature in said one fixture drops below a predetermined value, or when the suction pressure drops below a. predetermined value or the head pressure of the compressor rises above a predetermined value, means for controlling the fiow of refrigerant through the evaptemperature in one of said fixtures rises above apredetermined value, the suction pressure rises above a value indicating that all of the evaporators are defrosted, and the head pressure of the compressor drops below a predetermined value,

means for interrupting operation of the compressor whenever the temperature in'said one fixture drops below a predetermined value, or when the suction pressure drops below a predetermined value or the head pressure of the compressor rises above a predetermined value, thermostatic valve means for controlling the flow of refrigerant through the evaporator in another of said fix- .tures, and means responsive to acondition to be maintained in said other fixture for controlling the superheat setting of said valve means.

. 13. In a multiple fixturerefrigerating apparatus having an evaporator for each fixture, a. condenser and a compressor for circulating refrigerant through the evaporators, control means for said compressor, said control means including means for starting the compressor whenever the temperature in one of said fixtures rises above a predetermined value, the suction pressure rises above a value indicating that all of the evaporators are defrosted, and the head pressure of the compressor drops below a predetermined value, means for interrupting operation of the compressor whenever the temperature in said one fixture drops below a predetermined value, or when the suction pressure drops below a predetermined value or the head pressure of the compressor rises above a predetermined value, thermostatic valve means for controlling the flow of refrigerant through the evaporator in another of said fixtures, a second valve means for controlling the flow of refrigerant to said thermostatic valve means, and means responsive to the temperature in said other fixture for controlling the position of said second valve means to maintain the temperature in said other fixture at a desired value.

14. In a multiple fixture mechanical refrigerating apparatus having an evaporator for each fixture, a condenser and a compressor for circulating refrigerant through the evaporators, means responsive to the temperature of one of the fixtures for starting and stopping operation of the compressor to maintain desired temperature conditions Within said fixture, means responsive to the temperature in a second fixture for controlling the flow of refrigerant through the evaporator in that fixture to maintain the temperature therein at a desired value, means responsive to the humidity in a third fixture for controlling the fiow of refrigerant through the evaporator in the third fixture to maintain the humidity therein at a desired value, and means for always preventing restarting of the compressor until the suction presmeans responsive to the temperature in a second I fixture for controlling the flow of refrigerant through the evaporator in that fixture to maintain the temperature therein at a desired value, means responsive to the humidity in a third fixture for controlling the flow of refrigerant through the evaporator in the third fixture to maintain the humidity therein at a desired value, and means for always preventing restarting of the compressor until the suction pressure has risen to a predetermined value whereby simultaneous defrosting of all the evaporators is efiected.

ALWIN B. NEWTON. 

